a. Of or relating to radio waves with a wavelength less than 10 meters (33 feet).
b. Of or relating to optical pulses with typical durations of femtoseconds.
2. Of extremely short duration: an ultrashort flash.
3. Extremely short: an ultrashort skirt.
4. Of or relating to fixed-income investments with extremely short maturities, usually less than one year.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(Telecommunications) (of a radio wave) having a wavelength shorter than 10 metres
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
1. extremely short, esp. in duration.
2. (of a wavelength) smaller than 10 meters.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.